Susceptibility of Rhododendron to Azalea Lace Bug, Stephanitis pyrioides (Scott)1

Abstract The invasive azalea lace bug, Stephanitis pyrioides (Scott), is one of the most damaging insect pests of the genus Rhododendron, especially azaleas. Feeding by nymphs and adults reduces the aesthetic value of infested plants. Rhododendron spp. (L.) and cultivars are a major component of public and private landscapes in the Pacific Northwest, as well as other parts of the U.S.. Variability in the susceptibility of Rhododendron to S. pyrioides has been previously examined but generally on a limited number of Rhododendron species and cultivars. We measured the susceptibility of 71 Rhododendron species, varieties, and cultivars over two years, selecting plants across the phylogenetic tree of Rhododendron, and quantified the proportion of leaf damage caused by S. pyrioides. We observed that trichome presence did not predict S. pyrioides damage. Plants from the subgenus Azaleastrum were the significantly most susceptible subgenus, and all sampled plants from this subgenus had measurable damage. In contrast, plants from the subgenus Hymenanthes were the significantly least susceptible, and most Hymenanthes plants had no measurable damage. This study provides a guideline for using host plant resistance to S. pyrioides in plant selection, and emphasizes the potential for S. pyrioides management if susceptible azaleas are to be used in the landscape. Species used in this study: Azalea lace bug, Stephanitis pyrioides, Rhododendron spp.